Protoplanetary Disk

A protoplanetary disk is a flattened, spinning disk of gas and dust that surrounds a newly formed star. It forms because the collapsing cloud that created the star was rotating; material that could not fall straight onto the star spread out into a disk.

The disk is mostly gas — roughly 99% by mass — with about 1% dust. That dust is the raw material for rocky planets and the cores of giant planets. Most disks lose their gas within a few million years.

Radio telescopes such as ALMA have imaged many protoplanetary disks, revealing rings and gaps that may be carved by young planets.

Read more in Step 1: Gathering the materials.